High lead aluminium alloy

ABSTRACT

THIS INVENTION IS A BEARING ALLOY FOR ACTING AS A LINING ON A STEEL BACKING. GOOD BEARING PROPERTIES ARE GIVEN BY HAVING A HIGH PERCENTAGE, PREFERABLY BETWEEN 10% AND 12% BY WEIGHT, OF LEAD IN ALUMINUM. STRENGTH CAN BE GIVEN BY SOME SILICON AND SOME CALCIUM IMPROVES THE SOLUBILITY OF THE LEAD IN THE ALUMINUM AND UP TO 1% OF LITHIUM MAY BE ADDED TO GLOBULARIZE THE LEAD IN THE ALUMINUM.

United States Patent 3,827,882 HIGH LEAD ALUMINIUM ALLOY Kenneth Lloyd,Chesham and Anthony Dennis Michael, London, England, assignors to TheGlacier Metal Company Limited.

No Drawing. Continuation of application Ser. No. 807,425, Mar. 14, 1969.This application Sept. 24, 1971, Ser. No. 183,705

Claims priority, application Great Britain Mar. 15, 1968,

12,785/68. Int. Cl C22c 21/00 US. Cl. 75-138 3 Claims ABSTRACT OF THEDISCLOSURE This invention is a bearing alloy for acting as a lining on asteel backing. Good bearing properties are given by having a highpercentage, preferably between and 12% by weight, of lead in aluminium.Strength can be given by some silicon and some calcium improves thesolubility of the lead in the aluminium and up to 1% of lithium may beadded to globularize the lead in the aluminum.

This is a continuation of application Ser. No. 807,425 filed Mar. 14,1969, now abandoned.

This invention relates to an aluminium base alloy particularly for useas a bearing material, for example in thin shell bearings where thealloy requires to be bonded by rolling to a steel backing eitherdirectly or with an intermediated layer of metal foil, or after thebacking has been plated with say nickel or cobalt.

According to the present invention, a bearing alloy which may be bondedto a steel or other backing, comprises aluminium and more than 3% oflead by weight. Perhaps there may be 10%-20% of lead, and preferably10%-12%.

It has been discovered that such a bearing has a surprising ability tosurvive without pick-up or seizure, momentary contact with the journalwhen for any reason the oil film thickness becomes locally less than thesurface roughness. This property is known as compatibility. Whilesoftness of the material is a factor in obtaining this property, otherfactors are relevant, and the property is, in general, littleunderstood.

According to a feature of the invention an aluminium base alloy,suitable for use as a bearing alloy and capable of being bonded to asteel backing, contains by weight 0.5% to 11.3% silicon and by weightfrom 3% or 3.2% to 26% lead, the balance 'being aluminium except fornormal impurities and from 0 to 1% of each of one or more of theelements copper, nickel and manganese to improve the strength of thealuminium matrix, and from 0 to 3% of calcium to increase the solubilityof the lead in the aluminium. It would probably be necessary to have amuch higher proportion of calcium in the melt in order to get 3% in thecasting, because much calcium would be evaporated off at the necessarytemperature of the melt.

The silicon gives strength to overcome the effect of the high proportionof lead, but the maximum amount of silicon in the alloy should be notmore than about 12% by weight of the aluminium present, so that thealloy remains hypo-eutectic in structure. That is to say that since thesilicon is almost solely contained in the aluminium phase, if the leadcontent by weight were 20%, the total silicon content should not exceed9.6% by weight in the alloy otherwise the alloy could be hypo-eutecticand subsequent roll bonding of the material would be exceedinglydifiicult, if not impossible.

The silicon is present preferably as a proportion of 0.5% by weight ofthe alloy, in order to increase the 'ice strength, hardness, and wearresistance, properties of the alloy as Well as reducing its tendency toseizure and may increase the lead at which scurfing occurs.

The lead provides the surface properties required of a bearing alloy,but preferably the Whole alloy is of uniform composition, and is not ofthe defined composition at the bearing surface.

The aluminium base alloy according to the invention may contain a smalladdition of tin to the alloy. The lead phase in analuminium-lead-silicon alloy is almost pure lead since the solubility ofsilicon and aluminium in lead are very low. Pure lead is particularlyprone to corrosive attack especially by organic acids such as may bepresent in the lubricating oil of a plain bearing. The corrosionresistance of lead can be greatly improved by additions of small amounts(up to 6% by weight) of tin.

Accordingly this invention provides for an addition of tin such that theamount of tin in the lead phase is up to 6% and preferably 3%. Since thesolubility of tin in aluminium and silicon is extremely low, anyaddition of tin is almost entirely dissolved by the lead phase. Thus, toobtain a tin content of 3% by Weight in the lead phase a total additionof only 0.3% need be made to the complete alloy containing 10 %of leadby weight.

An alloy according to the invention may also include up to 1% by weightof the whole alloy of bismuth, and this will reduce the ductility of thelead and the lead and the tendency, when the alloy is roll bonded to asteel backing, to form long stringers of lead. The addition of bismuthwill cause these lead stringers to break up when the material is rolled.Tellurium may replace bismuth with a similar effect. Up to 1% by weightof the total alloy of cerium or lithium may be added to globularize thelead in the aluminium.

The invention includes a bearing comprising a layer of an alloy asdefined, and also a layer of the alloy bonded to a steel or otherbacking.

That aluminium-lead alloys have not been developed earlier for use asbearing alloys is due to the technical difficulties imposed on theirmanufacture by the abnormal configuration of the equilibrium diagram ofaluminiumlead and the large difference in their densities.

When the lead content in aluminium exceeds 2% by weight, during castingthe alloy passes through a temperature range where the aluminium andlead molten liquids are completely immiscible in one another and as aresult of the large density difference the lead sinks rapidly to thebottom. To achieve a homogeneous alloy, it may be necessary duringcasting to extract the heat from a vertical length of the solidifyingalloy at such a speed that the alloy solidifies very rapidly so as tominimise the time to pass through this temperature range. Such a processis possible, although difficult, on a small scale by producing chillcastings in a mould arranged in such a way as to cause the heat to beextracted vertically (i.e. not through the walls of the mould) andrapidly. An easier and more reliable method has been developed. PatentApplication I Io. 519,096, now Pat. No. 3,432,293 discloses a contmuouscasting method in which the alloy is introduced into the mould at atemperature at which aluminium and lead liquids are miscible and inwhich the melt is solidified rapidly creating a substantially verticaltemperature gradient such that the solidification isothermals aresubstantially horizontal and hence prevent the segregation in a verticalplane. Such a method is capable of producing aluminium-lead alloys ofhigh lead content uniformly and evenly dispersed as fine particles inthe alloy. The addition of silicon to the alloy made for reasons ofimproved bearing properties also effects an improvement in the surfacequality and lead distribution in billets made by this method. Thefineness of the lead particles, which is im- 3 portant for a bearingmaterial, is dependent on the speed at which the alloy is chilled fromthe homogeneous liquid through the two-immiscible-liquids region.

The invention may be carried into practice in various ways but twoalloys will be quoted by way of example.

EXAMPLE I The alloy was constituted of:

Percent by weight Lead Silicon 4 Copper 1 Tin /2 Calcium /2 AluminiumBalance EXAMPLE II Percent by weight Lead 12 Copper 1 Tin /2 Silicon /2Aluminium Balance In each case, the cast alloy had reasonabledistribution of the lead without its collecting into too large localpools. The bearings had long life with little wear and without seizing.

What we claim as our invention and desire to secure by Letters Patentis:

1. In an aluminum-lead bearing alloy consisting essentially of aluminumand from 10 to 26 wt. percent of lead, the improvement which consists inincluding therein lithium in an effective amount up to 1% by weight ofthe total alloy to globularize the lead in the aluminum.

2. A hearing alloy member capable of being bonded to a steel backing andconsisting essentially of aluminum, lead and lithium, the content oflithium being present in an effective amount up to 1% of the total alloyand sufficient to globularize the lead in the aluminum, the content oflead being from 10 to 26% by weight of the alloy.

3. A hearing alloy as claimed in Claim 1 including 0.5% of silicon.

References Cited UNITED STATES PATENTS RICHARD O. DEAN, Primary ExaminerUS. Cl. X.R.

